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I'm into a bit of historical research. I have a 1986 Panasonic DX-3000 bike with a loose bottom bracket. I haven't opened it up yet (I'll be ordering the required tools for the job while ordering the replacement bottom bracket) but I think the axle is pitted and needs to be replaced. Finding a replacement axle is not going to be easy, thus I am planning to replace it with a cartridge bottom bracket.

The frame has a 68 mm bottom bracket housing with (what looks like) BSA threads. The spindle is a JIS square taper. The only cartridge I find for these specs is the Shimano BB-UN300. However, I am a bit lost when it comes to choose the axle length. The current axle length is 116 mm and pretty much symmetric. The BB-UN300 axle lengths that comes closer are 115 mm and 117.5 mm which should both match pretty well. However, I don't find anywhere indication of the axle offset for these models.

Where can I find this information? Which one should I choose?

Is there anything better than the Shimano BB-UN300 that I can hope to be able to buy today in Europe (more precisely in Germany)?

Thank you!

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The modern Shimano cartridqe bbs are mostly symmetrical. 115mm would probably be best bet. 107 is asymmetrical as is one (or more) of the D- sizes.

Axles for cup and cone (and the cups) are still available in good quality. IRD recently had Tange produce a variety of these. There are other cheaper options too.

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    Tange and Miche, amongst others, also make cartridge bbs of excellent quality that are a good alternative to Shimano.
    – JoeK
    Jul 4 at 19:13
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    Thank you @joek Can you suggest an online shop that still sells this old stuff? I have been looking around extensively but all I was able to find that is most likely compatible with this bike is the Shimano BB-UN300 117.5 mm everything else is sold out but I may have been looking in the wrong places. Miche and Token do cartridges that may be better quality than the Shimano but I haven't found compatible axle lengths anywhere.
    – dnn
    Jul 4 at 19:39
  • ebay.co.uk/itm/194024320681
    – JoeK
    Jul 4 at 20:48
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    there are other cheap off-brands like RPM and SunRace making cartridge bottom brackets in the lengths you want but they are not usually very durable.
    – JoeK
    Jul 4 at 20:50
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What a gorgeous bike that is!! I was a senior in high school that model year and that DX-3000 was my dream bike. Especially loved the black and yellow color scheme, which was the same as my state's university who's football program at the time was emerging from decades of losing into national prominence. I rode a Panasonic Sport 500 at the time, but made the move to college with a mountain bike in tow.

Much googling has not yet revealed a perfect cartridge bottom bracket for replacement for your crankset, an SR SXC-200 double, 52-42. You should measure the chain line--the distance from the center of the bike to the middle of the 2 chainrings. You could measure the distance from the edge of the B shell to the center of the chainrings and add 34mm (½ the bb shell width) or alternatively, the distance from the edge of the seat tube to the middle point between rings and add ½ the seat tube diameter (probably 27.2 overall diameter). The chain line should be confirmed to be 43.5mm

With this information, combined with your noted threaded shell width and spindle length, a bike shop with an experienced mechanic should have the correct cartridge BB in your hand right quick. Despite many hits on Google I'm simply not coming up with something viable. Shimano made a square taper bb, model BB-UN52, that apparently came with a 116mm spindle option, but I believe those are probably hard to find and certainly out of production. As you've noted, the axle's offset is yet another aspect tough to find.

I've compiled a few links to some helpful information for your bike. The Specs for 1986 Panasonic DX-3000 listed here are identical to ones posted in the catalog, which I've linked to below.

1986 Panasonic Bike catalog

Even the venerable, Sheldon Brown's Bottom Bracket size chart and primer is of limited help and no information is listed for the SR brands of crankset.

This link from First Components installation of square taper bottom brackets also has options for cartridge BB's that may be higher quality than the Shimano one discussed. Other manufacturers exist as well whose offerings are both above and below Shimano level quality. One note: while this is an excellent tutorial on the installation of cartridge bearing bottom brackets with a brief primer on square taper spindle interfaces, it has one problem. The aspect of the tutorial I vehemently disagree with is the suggestion to utilize a torque wrench to break free the threads of the old cups from the frame. That is monumentally stupid advice even with the torque setting on high. The rationale given is the increased power afforded by the long handle of the torque wrench. A breaker bar or cheater bar slipped over a different wrench should be used for increased leverage. NEVER use a torque wrench in that manner.

With the info you've collected and confirmation of the 43.5mm chain line, you certainly should have what's required for a shop to set you up with a workable cartridge BB.

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  • Thanks @jeff. A quick measurement of the chain line comes in at about 47 mm. I would not be so sure that any mechanic in a shop would have correct advice: most shops I visit do not even have the tools to service a bike this old...
    – dnn
    Jul 4 at 22:12

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